Stihl MS 250 Chainsaw Won’t Start (5 Fixes Lumberjacks Swear By)
Let’s bust a myth right off the bat: just because a chainsaw sounds complicated doesn’t mean fixing it is complicated. I’ve seen countless folks, even seasoned lumberjacks, get intimidated when their Stihl MS 250 refuses to fire up. But trust me, often the solution is simpler than you think. I’ve spent years felling trees, processing firewood, and generally being knee-deep in sawdust, and I’ve learned that a systematic approach to troubleshooting is key. So, let’s dive into the five fixes lumberjacks swear by when their Stihl MS 250 refuses to cooperate.
Stihl MS 250 Chainsaw Won’t Start: 5 Fixes Lumberjacks Swear By
1. Fuel System Follies: Is it Getting Gas?
The most common culprit, in my experience, is a fuel issue. Think of it like this: a chainsaw engine is like a hungry lumberjack – it needs fuel to work.
The Problem: The engine isn’t getting enough fuel, or the fuel it’s getting is stale or contaminated.
The Fix:
- Fuel Tank Check: This is the obvious one. Make sure there’s fuel in the tank. I’ve seen experienced guys swear they filled it yesterday, only to find it bone dry. Use a fuel stabilizer like STA-BIL to keep your fuel fresh, especially if you don’t use your saw regularly.
- Fuel Cap Vent: A clogged fuel cap vent can create a vacuum, preventing fuel from flowing. Loosen the fuel cap slightly. If the saw starts, the vent is the issue. Clean the vent with compressed air or a small wire. I’ve used a straightened paperclip in a pinch – just be careful not to damage the vent.
- Fuel Filter Inspection: The fuel filter sits inside the fuel tank, connected to the fuel line. This little guy gets dirty quickly, especially if you’re using fuel from a jerrycan. I always recommend using a fuel filter funnel when pouring gas. Here’s how to check it:
- Drain the fuel tank.
- Use a bent wire or a specialized fuel filter removal tool (they’re cheap and worth it) to fish out the filter.
- Inspect the filter. If it’s clogged with debris, replace it. A new fuel filter is inexpensive insurance against future problems.
- Technical Specification: Stihl fuel filters typically have a micron rating of 20-40 microns. This means they filter out particles larger than 20-40 millionths of a meter. If you’re using fuel with a higher ethanol content (over 10%), I recommend replacing the filter more frequently as ethanol can degrade rubber and plastic components.
- Fuel Line Examination: Check the fuel lines for cracks, kinks, or leaks. These lines can dry out and crack over time, especially in hot weather. If you find any damage, replace the fuel lines.
- Technical Tip: Fuel lines are typically made of Tygon or similar fuel-resistant material. When replacing them, make sure you use fuel-resistant lines specifically designed for chainsaws. Using the wrong type of hose can lead to premature failure.
- Carburetor Cleaning: This is where things get a little more involved, but it’s often necessary. The carburetor mixes fuel and air, and if it’s clogged, the engine won’t start.
- Locate the carburetor. It’s usually mounted on the side of the engine.
- Remove the air filter and the carburetor cover.
- Carefully disconnect the fuel lines and throttle linkage.
- Remove the carburetor.
- Use carburetor cleaner to thoroughly clean all the jets and passages. Pay special attention to the high- and low-speed jets. You can use a small wire to clear any stubborn clogs.
- Reassemble the carburetor and reinstall it on the engine.
- Personal Experience: I once had a Stihl MS 250 that refused to start after sitting idle for a few months. I disassembled the carburetor and found a tiny piece of debris blocking the low-speed jet. After cleaning it out, the saw fired right up.
- Data Point: Studies have shown that using fuel with ethanol content higher than 10% can lead to carburetor corrosion and fuel line degradation in small engines. Always use fuel stabilizer and consider using ethanol-free fuel whenever possible.
Safety Note: Always work in a well-ventilated area when dealing with gasoline. Wear gloves and eye protection. Dispose of used fuel properly.
2. Spark Plug Shenanigans: Is There a Spark?
If the fuel system seems okay, the next step is to check the spark plug. No spark, no start. It’s that simple.
The Problem: The spark plug is fouled, damaged, or simply not firing.
The Fix:
- Spark Plug Removal: Locate the spark plug. It’s usually on the top of the engine, near the cylinder head. Use a spark plug wrench to remove it.
- Visual Inspection: Examine the spark plug. Look for cracks, carbon buildup, or excessive wear. A healthy spark plug should have a clean, dry electrode. If the spark plug is fouled with carbon, clean it with a wire brush or replace it.
- Technical Specification: The correct spark plug gap for a Stihl MS 250 is typically 0.020 inches (0.5 mm). Use a spark plug gap tool to ensure the gap is correct. An incorrect gap can lead to poor performance or starting problems.
- Spark Test: Connect the spark plug to the spark plug wire. Hold the spark plug against the engine block (grounding it). Pull the starter cord. You should see a strong, blue spark. If you don’t see a spark, the spark plug is bad and needs to be replaced.
- Safety Note: Be careful not to touch the spark plug while pulling the starter cord. You could get a shock.
- Ignition Coil Check: If you’re not getting a spark with a new spark plug, the problem may be with the ignition coil. The ignition coil generates the high voltage needed to create a spark. Testing the ignition coil requires a multimeter.
- Disconnect the spark plug wire from the spark plug.
- Set the multimeter to measure resistance (Ohms).
- Connect one probe of the multimeter to the spark plug wire connector on the ignition coil.
- Connect the other probe to the engine block (ground).
- You should get a reading of several thousand Ohms. If you get a reading of zero or infinity, the ignition coil is bad and needs to be replaced.
- Personal Experience: I had a chainsaw that would start intermittently. After replacing the spark plug and still having issues, I tested the ignition coil and found that it was failing. Replacing the ignition coil solved the problem.
3. Compression Conundrums: Is the Engine Sealed?
Compression is essential for an engine to run. If the engine isn’t sealed properly, it won’t be able to compress the air-fuel mixture, and it won’t start.
The Problem: Low compression due to worn piston rings, a damaged cylinder, or leaky valves (though valves are rare in a 2-stroke engine).
The Fix:
- Compression Test: A compression test will tell you if the engine is sealing properly. You’ll need a compression tester for this.
- Remove the spark plug.
- Screw the compression tester into the spark plug hole.
- Pull the starter cord several times.
- Read the compression reading on the gauge.
- Technical Specification: A healthy Stihl MS 250 should have a compression reading of at least 120 PSI (pounds per square inch). If the compression is below 100 PSI, the engine likely has a compression problem.
- Troubleshooting Low Compression: If the compression is low, there are a few things you can check:
- Piston Rings: Worn piston rings are a common cause of low compression. To check the piston rings, remove the cylinder head and inspect the piston and rings. If the rings are worn or broken, they need to be replaced.
- Cylinder Damage: A damaged cylinder can also cause low compression. Inspect the cylinder walls for scratches or scoring. If the cylinder is damaged, it may need to be re-bored or replaced.
- Gasket Leak: Check the cylinder head gasket for leaks. A leaking gasket can cause low compression. If the gasket is leaking, it needs to be replaced.
- Case Study: I once worked on a Stihl MS 250 that had very low compression. After disassembling the engine, I found that the piston rings were completely worn out. Replacing the piston rings restored the engine to its original performance.
- Two-Stroke Specific Considerations: Unlike four-stroke engines, two-stroke engines don’t have valves. Compression issues are almost always related to the piston, rings, or cylinder.
Important Note: Repairing compression issues often requires specialized tools and knowledge. If you’re not comfortable working on the engine yourself, it’s best to take it to a qualified mechanic.
4. Air Filter Annoyances: Is it Breathing?
A clean air filter is crucial for proper engine performance. A clogged air filter restricts airflow, which can lead to starting problems, poor performance, and even engine damage.
The Problem: The air filter is clogged with dirt, sawdust, or other debris.
The Fix:
- Air Filter Inspection: Locate the air filter. It’s usually located under a cover on the top or side of the engine. Remove the air filter and inspect it. If it’s dirty, clean it or replace it.
- Cleaning the Air Filter:
- Foam Filters: Foam air filters can be cleaned with warm soapy water. Rinse the filter thoroughly and allow it to air dry completely before reinstalling it. I like to add a light coating of air filter oil after cleaning to improve its filtering ability.
- Felt or Paper Filters: Felt or paper air filters can be cleaned by tapping them gently or using compressed air. Be careful not to damage the filter. If the filter is heavily soiled, it’s best to replace it.
- Technical Tip: Avoid using gasoline or solvents to clean air filters. These can damage the filter material.
- Air Filter Replacement: Air filters are relatively inexpensive, so it’s a good idea to replace them regularly, especially if you use your chainsaw frequently in dusty conditions.
- Data Point: Studies have shown that a clogged air filter can reduce engine power by up to 20%. Regularly cleaning or replacing the air filter can improve engine performance and fuel efficiency.
5. Starter System Snafus: Is it Engaging?
The starter system is responsible for turning the engine over so it can start. If the starter system is malfunctioning, the engine won’t start.
The Problem: A faulty starter cord, recoil spring, or starter pawls.
The Fix:
- Starter Cord Inspection: Check the starter cord for fraying, breaks, or knots. A damaged starter cord can break, making it impossible to start the engine. If the cord is damaged, replace it.
- Recoil Spring Check: The recoil spring is responsible for retracting the starter cord. If the recoil spring is broken or weak, the starter cord won’t retract properly. To check the recoil spring, pull the starter cord out a few inches and release it. The cord should retract smoothly and quickly. If it doesn’t, the recoil spring needs to be replaced.
- Starter Pawl Examination: The starter pawls (also called dogs or catches) engage with the flywheel to turn the engine over. If the starter pawls are worn or damaged, they may not engage properly, preventing the engine from starting. To check the starter pawls, remove the starter assembly and inspect the pawls. If they are worn or damaged, replace them.
- Technical Tip: Lubricate the starter pawls with a light grease to ensure smooth operation.
- Flywheel Key Shear: While less common, a sheared flywheel key can also cause starting problems. The flywheel key aligns the flywheel with the crankshaft. If the key shears, the timing will be off, and the engine won’t start. To check the flywheel key, remove the flywheel and inspect the key. If it’s sheared, it needs to be replaced. This often happens if the saw experiences a sudden stop, like hitting a rock or nail.
- Personal Experience: I once had a chainsaw that was very difficult to start. After checking everything else, I discovered that the flywheel key was partially sheared. Replacing the key solved the problem.
Preventive Maintenance:
Beyond these five fixes, remember that prevention is always better than cure. Regular maintenance will help keep your Stihl MS 250 running smoothly and prevent starting problems in the first place.
- Regular Cleaning: Keep the chainsaw clean, especially the air filter, cooling fins, and spark plug area.
- Proper Fuel Storage: Store fuel in a clean, airtight container and use a fuel stabilizer.
- Sharp Chain: A sharp chain reduces strain on the engine and makes starting easier.
- Professional Servicing: Consider having your chainsaw professionally serviced at least once a year.
Wood Processing Insights: Matching Tool to Task
Choosing the right chainsaw for the job is crucial for efficiency and safety. The Stihl MS 250 is a versatile saw, well-suited for felling small trees, limbing, and cutting firewood.
- Log Diameter: The MS 250 is ideal for logs up to 12-14 inches in diameter. Trying to cut larger logs can strain the engine and increase the risk of kickback.
- Wood Type: While the MS 250 can handle both hardwoods and softwoods, it’s best suited for softwoods like pine and fir. Hardwoods like oak and maple require more power and can wear the chain down faster.
- Firewood Preparation: When cutting firewood, aim for consistent lengths to make stacking and burning easier. I typically cut my firewood into 16-inch lengths, which fit well in my wood stove.
- Technical Tip: Use a measuring stick or a jig to ensure consistent firewood lengths. This will save you time and effort in the long run.
- Industry Standard: The recommended moisture content for firewood is below 20%. Use a moisture meter to check the moisture content before burning. Burning wet firewood can lead to creosote buildup in your chimney, which can be a fire hazard.
- Data Point: Different wood species have different heat values. For example, oak has a higher heat value than pine. Knowing the heat value of your firewood can help you optimize your wood-burning efficiency. A cord of seasoned oak can produce approximately 24 million BTUs (British Thermal Units) of heat, while a cord of seasoned pine produces around 16 million BTUs.
Safety First!
No matter how experienced you are, always prioritize safety when working with a chainsaw.
- Personal Protective Equipment (PPE): Always wear appropriate PPE, including a helmet, eye protection, hearing protection, gloves, chainsaw chaps, and steel-toed boots.
- Kickback Awareness: Kickback is a sudden, uncontrolled movement of the chainsaw bar that can cause serious injury. Be aware of the risk of kickback and use proper cutting techniques to avoid it.
- Safe Cutting Practices:
- Maintain a firm grip on the chainsaw with both hands.
- Keep your feet firmly planted and maintain a stable stance.
- Avoid cutting above shoulder height.
- Be aware of your surroundings and watch out for obstacles.
- First Aid Kit: Always have a well-stocked first aid kit on hand.
- Emergency Plan: Have an emergency plan in place in case of an accident.
Final Thoughts
Troubleshooting a chainsaw can seem daunting, but with a systematic approach and a little bit of knowledge, you can often diagnose and fix the problem yourself. Remember to always prioritize safety and don’t be afraid to seek professional help if you’re not comfortable working on the chainsaw yourself. By following these tips and practicing regular maintenance, you can keep your Stihl MS 250 running smoothly for years to come. Now get out there and make some sawdust! I hope that you find this guide helpful and that you are able to get your chainsaw running quickly.
